Over time, the value of some coin materials have increased to be worth more than the face value of the coins. Steel is an attractive alternative material for replacing some current coin alloys—primarily because of steel's low cost and excellent durability. The current price of steel is only about 1/10 to 1/15 of the price of copper. However, steel has a high permeability (i.e. degree of magnetism) and other problematic electrical and surface-hardness properties. Specifically, steel's lag phase angle is completely different from non-ferromagnetic materials. Consequently, existing coin validators will not recognize (for example) a steel quarter—even though the steel quarter may have the same dimensions and stamping as currently-circulating quarters.
However, some steel alloys are non-ferromagnetic and have significantly different properties than common steel. To use most steels, stamping tonnage must be increased by more than 20% (relative to copper or cupronickel) to achieve a clean stamping relief result. To be usable, a steel coin must have low strain hardening properties (i.e. be sufficiently soft) for effective stamping, and have a relative permeability that is close to 1.0. A relatively high nickel-steel coin can meet these criteria. If steel containing 18% nickel and 0.60% carbon is quenched in water, the material will be perceptibly softened. If the amount of nickel is raised to 25%, this softening is even more apparent. Generally, as the amount of nickel increases, the steel softens, and a 25% nickel steel can be worked cold almost as easily as German silver or cupronickel.
The need exists for a replacement alloy material that is less expensive and more durable (among other things) than the cupronickel coin cladding material that is currently in use. As described herein, the inventors determined that, by manipulating various steel alloys, a nickel steel alloy could be identified and developed for use as an alternative coin cladding material for coins such as US dimes, quarters, half dollars, and dollar coins. The material described herein meets that criteria and is compatible with coin validator/acceptor machines currently in use.